The production of hydrocarbons, such as oil and gas, has been performed for numerous years. To produce these hydrocarbons, a production system may utilize various devices, such as tubular members, within a well. Typically, the tubular members are placed within the wellbore to provide structural support, zonal isolation, and allow for communication between subterranean formations and surface facilities. That is, the tubular members may provide flow paths for formation fluids, such as hydrocarbons, within the wellbore and to facilities located at the surface. As these tubular members are individual sections of pipes, two or more tubular members may be joined together by threaded connections or welds to provide this functionality within a well.
For the threaded connections, two distinct classifications are utilized, which are API (American Petroleum Institute) and premium connections. API connections typically rely on entrapment of thread compound in the helical thread paths to provide sealability. See U.S. Pat. Nos. 5,411,301 and 5,212,885. Alternatively, premium connections typically rely on a metal-to-metal seal formed by the threaded connections to provide sealability. See U.S. Pat. No. 6,041,487. These metal-to-metal seals are integral to the design of the connectors of the tubular members.
Regardless of the classification, threaded connections in a wellbore are generally designed to maintain structural integrity and sealability performance during the life of the well for various environmental and safety reasons. For example, sealability is one performance characteristic of the threaded connection that describes how pressurized reservoir or injection fluids are contained within the tubular member. Sealability performance of the threaded connections is affected by, among other things, the fluids being transported, temperature, pressure, tensile and compressive loads, bending, surface finish, thread compound, base material properties, connection geometry, make-up torque and other factors. Also, the threaded connections are exposed to different conditions during make-up, during placement into the wellbore, and/or during production and injection cyclic loading. As such, sealability is one performance measure that may be assessed during evaluation of the threaded connections formed by different tubular members.
Various methods may be utilized to assess the performance of the threaded connections. One method for evaluating performance of a threaded connection is to physically test the threaded connection under possible conditions expected during its lifetime. For this method, an understanding of anticipated field operations should be considered to provide performance results that accurately reflect the environment that the threaded connection is likely to experience. Because of the complexity, physical testing is expensive and time consuming, often taking several months to complete with costs of several hundred thousands of dollars.
A second method for evaluating performance of a threaded connection may include finite element analysis (FEA). FEA may assess the contact characteristics of connection features (i.e. the metal-to-metal seals, threads, etc.) as well as the stress-strain response of the threaded connection under varying load conditions. While the FEA method is generally inexpensive and not time consuming, assessing threaded connection performance based solely on computational criteria may be misleading. For instance, the FEA method does not capture micro-mechanisms, such as surface interactions during make-up. In some evaluations, a false positive is achieved, indicating that the computational criteria are met for a specific load, but subsequent physical testing indicates that the threaded connection does not achieve the predicted performance. In other evaluations, physical testing may reveal adequate performance, while the computational criteria of the FEA method were not satisfied. Finally, while FEA may be used to assess stress-strain response, it may not be used to explicitly assess the impact of certain parameters, such as thread compound and surface finish, on performance. As such, while using a FEA only method to evaluate threaded connection performance reduces the amount of time and cost to identify candidate threaded connections for a given application, the individual threaded connections are generally each physically tested to ensure adequate performance.
A third method for evaluating performance of a threaded connection is to use FEA in combination with limited physical testing. See Hilbert et al., “Evaluation of Premium Threaded Connections Using Finite-Element Analysis and Full-Scale Testing,” SPE 23904 (1992). This method utilizes a standardized test program to verify the integrity of the threaded connections. A result from this type of evaluation is typically valid for any application (i.e., not specific to an individual well or loading condition). However, extrapolating the results from one test program of one connection geometry (i.e., diameter and wall thickness) to a different geometry is challenging and problematic. In addition, the cost associated with performance assessment of geometrically similar threaded connections is high.
An example of this method includes the commercial use of an FEA criteria to evaluate sealability in the United States in 2004. In this use, the sealability criteria were developed from comparisons of seal versus leak behavior exhibited during physical testing with behavior predicted by FEA. The FEA criteria were then applied to FEA results from subsequent connection evaluations to assess load and pressure combinations at which adequate sealability performance was expected. These results were then placed into a database and used to make commercial decisions about equipment purchases.
Further, although the approach described above has typically been used for the evaluation of individual threaded connections, it was also applied in 2004 to the evaluation of connection groups in the United States. In this application, physical testing was performed on threaded connections at the geometric extremes of a group. The FEA results were utilized for commercial purposes to aid in interpolation of sealability between these extremes for other threaded connections. These results were then placed into a database and used to make commercial decisions about equipment purchases.
Limitations of the prior evaluation methods include (1) the lack the proper scalability for the individual threaded connections; and (2) the expense or time consumed by the methods. Also, threaded connections contained in the evaluation group were not selected based on any criteria to ensure that their individual performance limits should be similar to other threaded connections in the group. As such, the need exists for a method for evaluating a group of threaded connections with the specificity of physical testing, simplicity of FEA testing, and clarity of performance limits that account for the various factors governing connection performance.
Other related material may be found in at least U.S. Patent Application Publication No. 2003/0178847; U.S. Pat. No. 6,607,220; U.S. Pat. No. 6,363,598; U.S. Pat. No. 6,176,524; U.S. Pat. No. 6,123,368; U.S. Pat. No. 6,041,487; U.S. Pat. No. 5,895,079; U.S. Pat. No. 5,689,871; U.S. Pat. No. 5,661,888; U.S. Pat. No. 5,411,301; U.S. Pat. No. 5,212,885; U.S. Pat. No. 4,962,579; and U.S. Pat. No. 4,707,001.